1. Field of the Invention
This invention is related to wafer bonding for optoelectronic applications. More particularly, the invention relates to a (Al, Ga, In)N and ZnO direct wafer bonding structure for highly efficient (Al, Ga, In)N based light emitting diodes and for optoelectronic applications, and its fabrication method.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification. A list of these different publications can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Wafer bonding technology using different combinations of materials, such as InP/GaAs, AlGaInP/GaP, GaAs/GaN, ZnSSe/GaN, has been studied for applications in optoelectronic integration, light emitting diodes (LEDs), vertical cavity surface emitting lasers (VCSELs), and electronic devices [1,2,3,4].
In a nitride LED system, there are several reports of fabricating transparent electrodes on a p-type GaN layer. The general method is to use thin metals of Ni and Au [5]. Because of the light absorption in the metal, transmittance is only around 60%. Also, surface feature shaping for improving light extraction efficiency is difficult because of the hardness of GaN material and the instability of p-type GaN conductivity.
Another approach is to use Zinc Oxide (ZnO) layer growth on p-type GaN [6]. However, this method requires using ZnO crystal growth equipment and ultra-high vacuum conditions. Moreover, it is difficult to grow the thick layers, e.g., ˜500 μm thick layers, that are suitable for feature shaping for the purpose of light extraction.
What is needed are improved methods of wafer bonding in the above-identified material systems. The present invention satisfies that need, and comprises the first demonstration of a direct wafer bonding between (Al, Ga, In)N and ZnO wafers.